Giornata di Studio
con CNRS Francia
Sedimentary archives to infer ecosystem response to disturbance
Michel MAGNY, and LAMA Members
North-south palaeohydrological contrasts in the central Mediterranean during the Holocene: tentative synthesis and working hypotheses
On the basis of a multi-proxy approach and a strategy combining lacustrine and marine records along a north-south transect, data collected in the Central Mediterranean within the framework of a collaborative project have led to reconstruction of high-resolution and well-dated palaeohydrological records and to assessment of their spatial and temporal coherency. Data give evidence of contrasting palaeohydrological patterns operated throughout the Holocene, both on millennial and centennial scales. Comparison between available palaeohydrological data for the whole Mediterranean suggests possible influences of forcing factors and general atmospheric circulation patterns.
Subfossil chironomids in paleolimnology: from the inference of temperature changes to the reconstruction of lake functioning history
In lakes, chironomid larvae (Insecta Diptera) are benthic organisms that produce chitinous remains (head capsules) during their development. Past changes in communities are reconstructed after extraction and identification of head capsules preserved in the sediment. Chironomid assemblages are potentially affected by a variety of environmental conditions interacting in complex ecological processes. Inferring temperature changes from a chironomid sequence using a transfer function assumes that the chironomid assemblages respond, directly or indirectly, to temperature. We will present temperature reconstructions for the last 1500 years derived from chironomid records of three neighboring lakes in the Northern French Alps. In addition to temperature, the most commonly recognized influencing factors are trophic status, oxygen conditions and organic matter in the sediment. In the bottom of deep stratified lakes, the sensitivity of the bottom community to changes in oxygen availability derives from the differential behavioural and/or physiological adaptations of the taxa to survive under hypoxia of variable degree. As a last example, we will present the results from the multiproxy study (IPER-RETRO project) carried out at Lake Annecy (French Alps).
Current states and ecological trajectories of lakes over the last 1500 years: the study of the biological and biogeochemical responses to disturbances
The evolution of lake is determined by “natural” (climate, lake ontogeny) and “anthropic” (agricultural development, fish introduction, pollutants…) factors (Leavitt et al., 2009). Because monitoring records exist since the early XX° century for only a few lakes, paleolimnological studies are key approaches to understand the response of ecosystems to disturbance. We conducted a multi-proxy paleolimnological investigation to understand: (i) the biological response (Chironomid assemblages) and (ii) the changes in carbon cycle (in particular methanogenesis). 15 lakes, belonging to different typologies and presenting different stories in land use and occupation, have been studied from Jura Mountains to Greenland
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